1. Field of the Invention
The present invention relates, in general, to methods and systems for radio frequency identification (RFID) tags, and, more particularly, to systems and methods for providing multiple diverse band antennas in an integrated module.
2. Description of the Related Art
Radio Frequency identification (RFID) is gaining popularity in a variety of manufacturing and service applications. In passive RFID applications, an RFID reader transmits a modulated radio frequency (RF) signal to the RFID tag. Passive RFID tags comprise an antenna that receives power transmitted from the reader and couples that power to be used by on-tag circuitry. In a typical implementation, the on-tag circuitry modulates the input impedance coupled to the antenna between strongly matched and strongly mismatched states which can be detected by the reader to communicate data between the reader and the tag.
RFID has a number of standard frequency ranges, each of which offer varying performance characteristics. For example, high frequency (HF) operated in a 10-15 MHz range while ultra high frequency (UHF) operates in a 850-950 MHz range. In the HF frequency range, tags are primarily responsive to the near-field magnetic component of an electromagnetic emission from the reader. Because near-field communication is limited to a few inches around a reader there is an inherent security benefit to HF RFID operations. In the UHF frequency range, tags are primarily responsive to far-field electric field components. Electric fields travel farther in air than magnetic fields and so are useful to read tags at a greater distance from the reader, but are more sensitive to interference from conductive obstacles, such as metal and high water content obstacles such as people, animals and, to a lesser extent foliage, humidity, and fog that will absorb the electric field.
In large part RFID tags support a single frequency band which forces the user to select between either HF or UHF operation. While this is acceptable for many product identification type applications, it is constraining for RFID applications in service industries where both near-field and far-field communication is desired. HF and UHF antenna designs are significantly different, which has made packaging them in a single device uncommon. HF tags often use a printed loop antenna that is made with as large a diameter as practical for the application to improve the capture of magnetic energy. UHF designs may use patch antennas, microstrip antennas, inverted-F antennas or other types. It is generally desired to increase the surface area of the antenna so as to increase the magnitude of the captured electric field.
Robust wearable RFID tags present further mechanical and electrical challenges. Many RFID tag designs for product tracking, for example, are intended for short term or disposable applications that require modest durability. In service industry applications, it may be desirable to have an RFID tag last for days or even years. Moreover, wearable RFID tags that are worn as a part of clothing or an item of jewelry are desired but create form factor and mechanical flexibility challenges.